麻豆视频

Great egrets usually hunt in shallow water, stalking small fish, which they swallow whole

The great egret, Ardea alba, is a tall and stately bird, graceful in flight,听

听deliberate and stealthy when hunting. It is a magnificent sight and entertaining to watch, making it a favorite with birders. But in the 1800s its brilliantly white feathers and long, extravagant plumes inspired devastating hunting, wiping out heronries in a single day and driving the species to the brink of extinction in North America. Dread of losing this and many other species led to legislation curtailing the feather trade, establishing the great egret's current association with conservation movements.听

Great egrets grow to 38 inches tall and have little sexual dimorphism. All of its feathers are white, and its legs and feet are black. The beak is orange and the patch of bare skin between the beak and eyes, the lore, is yellow. Breeding season produces a major transformation in plumage and smaller changes in color. The lore changes from yellow to brilliant lime green, and long, graceful plumes called aigrettes grow from the shoulder areas to trail over the back. Each aigrette is composed of about 35 strands of slim feathers.听

Males also develop a dark line running the full length of the top of the beak.听

In the 1870s Victorian ladies of fashion in America and England took to wearing extravagant hats adorned with feathers or even whole stuffed birds. Aigrettes were used extensively, and when overhunting made egrets rare, cost of an ounce of aigrettes rose to be equivalent of the cost of an ounce of gold. Aigrettes were judged to be so beautiful that harvesting was widespread and thorough, driving great egrets to the brink of extinction.听

By 1886, it was estimated that 5 million great egrets had been killed for their feathers, for fashion. Fortunately, the public became aware of the overhunting of great egrets and many other species--about 50 bird species were being killed solely for their feathers, used to adorn hats and fishing lures. The Migratory Bird Treaty Act became law in 1918, prohibiting harvesting and sale of bird feathers.听 The Audubon Society, established in 1905 for the conservation of waterbirds and to oppose the feather trade, adopted the image of a flying great egret as its symbol in 1953. Great egrets have increased in numbers since protection became effective, but establishment of new breeding populations has been slow. For example, great egrets began breeding in salt marshes on Nantucket in the 1970s. Populations in Europe have been rebounding and expanding since the 1980s, where they have begun breeding in 13 countries, including England, Sweden and Finland.听

It is difficult to manage what has not been precisely defined. Great egrets are native to every continent except Antarctica, and currently four subspecies are recognized in Asia, Africa, the Americas, and southern Europe.听 But morphological and behavioral data suggest that some of these subspecies may be designated as separate species when genetic data become available.听 Hopefully, that will be soon.

Great egrets usually hunt in shallow water, stalking small fish, which they swallow whole. They also take frogs, crayfish, dragonflies and grasshoppers when the opportunity arises. They build large nests of sticks lined with plant material. Nests are in trees beside extensive wetlands with large reed beds. They nest colonially and colonies frequently include other wading bird species, such as great blue herons and snowy egrets.听

While on sabbatical at UC Davis, I frequented the Yolo Bypass Wildlife Area to watch birds, and great egrets were always present, usually stalking prey. Between Grand Junction and Moab I watched a great egret standing motionless in riffles in the Colorado River, waiting to stab and gulp. It was a model of patience, but after 15 minutes it gave up and lifted gracefully, circled and headed upriver. Regrettably, great egrets are isolated and infrequent in Colorado, but census figures give us optimism that they are increasing. Boulder Audubon reports that the North American Breeding Bird Survey saw a 2.5% increase per year between 1966 and 2011. They reside reliably in summers at a large heronry at Saint Vrain State Park, and they are seen hunting at Union Reservoir, Boulder Reservoir, and Walden Ponds. Finally, and perhaps best of all, two new nesting colonies have become established in the last two decades.听